The present invention is directed to power burners whose air is supplied by a fan and motor and, in particular, to oil burners, gas burners and dual-fuel burners of any practical size and having improved manually adjustable air flow mechanisms.
Conventional burners generally include an air tube having a fuel supply conduit (or two for dual fuel) extending axially within the tube. Each fuel supply conduit is connected at one end to a fuel supply pump or gas manifold and terminates at the other end near the end of the air tube where the fuel is dispensed as an oil spray or gas. The fuel is mixed with the air which has been delivered by a motor powered blower. A burner-mounted ignition system is connected to an ignition apparatus that is located adjacent to the fuel nozzle near the exit end of the air tube where it ignites the fuel-air mixture.
Burners of these types employ various mechanisms for adjusting air flow. For example, an oil burner disclosed in U.S. Pat. No. 5,184,949 employs an air gate disposed downstream of the blower for controlling the flow through an air flow passage. The position of the head may be adjusted. This fails to disclose a mechanism to control the total flow while simultaneously controlling the pressure behind the flame retention head. This pressure is important for reliable ignition and flame stability.
U.S. Pat. No. 4,651,928 to Schmitt discloses a mechanism that modulates the fuel flow by changing fuel pressure and temperature to follow the load requirement and correspondingly adjusts the air both downstream of the blower and near the nozzle to match the fuel flow by using a system of bellows with return springs. A servo control package is also included.
Burners built according to U.S. Pat. No. 4,651,928 appear more complex, more expensive, and less reliable than typical European burners, which are usually more complicated than typical North American burners. Typical North American oil burner service departments would not accept such a burner into their markets, in light of the requirement to understand and service unfamiliar and complex servos and special controls.
Historically, oil burner manufacturers have taken one of two approaches to making burners. One approach is to make a standard chassis (motor-blower with fuel pump, ignition transformer and control all pre-wired), and then provide individual air tube combinations with specified air-handling parts to match the needs of the particular furnace or boiler. These parts are determined by laboratory application tests done jointly by the burner manufacturer with the boiler or furnace manufacturer. This approach requires a large inventory of parts and a long and costly effort to get to market.
The start up of a boiler or furnace with this type of burner requires only a simple air band or air shutter adjustment. But if a lower firing rate is desired (viz., house insulation added) the technician should change the parts as specified by the manufacturer for the lower rate which he might not be familiar with or not have readily available.
The second approach to making a burner is to make a standard chassis and a standard air tube and end cone assembly plus a standard adjustable and removable drawer assembly (fuel conduit with electrodes, nozzle and nozzle adapter, and flame retention head) similar to the burner disclosed in U.S. Pat. No. 4,484,887. A common drawback with this approach has been that both the drawer assembly and the air band (or air throttle) are each adjusted separately by the installer.
Needed is a simple, low cost, reliable, efficient burner designed to operate over a wide range using a relatively high performance blower (i.e.: with high pressure and minimal watts) and using as many standard parts as is practical, which is easy for the installer to set up and adjust properly.
In general, the present invention is directed to a burner comprising a motor driven blower in a housing. An air tube has an inlet end portion and an outlet end portion and may be mounted to the housing. The housing forms an air flow path between the blower and the air tube. In an oil burner, a conduit feeds liquid fuel under pressure to the nozzle at the outlet end portion of the air tube where it sprays the fuel.
One aspect of the invention includes two throttling devices affixed to the fuel conduit coaxial to the air tube, each consisting of a tapered ring and a disk located within the ring and coaxial with it. Throttling together they control the air flow to a value proper for the fuel-input rate. The upstream throttle ring is configured to reduce the upstream pressure to a value determined to provide air to the second plate (the retention plate) to an exit velocity just low enough for reliable ignition and flame stability.
Both throttle rings may have tapers that are converging or diverging. Both minimum and maximum firing rates may be achieved by configuring the cones properly. The adjustment direction for converging and diverging cones should be opposite to one another however.
A mechanism is connected to the fuel conduit (a portion of which is preferably external to the housing) to accurately move it axially, thereby controlling the positions of the rigidly affixed throttle plate and the retention plate simultaneously. Consequently, only a single adjustment setting is needed for any firing rate within the range of the burner.
Referring to more specific features of the invention, the air flow control device adjusts the flow rate and two pressures in the air tube, P1 and P2. P1 is the pressure delivered by the blower. It is high at low flows and diminishes more or less uniformly as the flow increases. P2 is the pressure after the first air flow restrictor, and should be quite low at low rates and gradually higher at higher rates to assure good ignition and stability as the air accelerates through the second air flow restrictor to the flame zone where the pressure is near zero. This means that the throttle ring should close down to the throttle plate at the minimum setting where P1 is high, and should open up rapidly with the flow rate as P1 falls while P2 needs to rise.
A preferred configuration of the first air flow restrictor consists of a round throttle plate surrounded concentrically by a throttle ring, forming a venturi which is carefully configured to maintain P2 as described above. A preferred configuration of the second restrictor consists of a round retention head surrounded by a conical retention ring, forming a venturi, which is tapered to produce the minimum and the maximum flow rates required while P2 varies as specified for stability. In the preferred embodiment, the throttle plate and the retention plate are affixed to the fuel conduit and concentric with the air tube and at a fixed axial distance apart. Also, the throttle ring and retention head are affixed to the air tube at the same fixed axial distance apart. As the adjusting mechanism moves the fuel conduit axially, the throttle plate and retention plate are displaced equally within their respective concentric rings to accurately control the flow and maintain P2 for stable combustion and reliable ignition.
An added advantage of this invention relates to the improved uniformity and higher combustion efficiency of the flame. This results from improved air distribution in the air tube after the throttle where air approaches the flame retention head. To enhance this, several holes are incorporated in the throttle plate.
The present invention advantageously enables air pressure to be simply yet precisely controlled with the air flow control device. A user need not make an adjustment near the blower and a separate adjustment in the air tube. Instead, one air flow control device may be used to meter air pressure and air flow at locations near the nozzle and between the blower and the nozzle. This advantageously achieves a desirable range of pressure near the nozzle and results in uniform air flow. The present invention advantageously may adjust air pressure and flow to a desired level using only the air flow control device, although additional adjustment mechanisms may be used, if desired.
In a preferred embodiment of the present invention, the burner includes an air flow control device comprising a first air flow restrictor disposed between the blower and the nozzle, a second air flow restrictor disposed downstream of the first air flow restrictor relative to the direction of air flow, and a mechanism adapted to adjust the position of both the first and second restrictor plates to control air flow. The mechanism comprises a component connected to the conduit and a member that engages the component so as to move it precisely in either direction. The mechanism and the connected portion of the conduit are preferably external of the housing.
In one aspect of the invention the mechanism comprises an apertured support that extends outwardly from the housing. The mechanism component comprises an arm that is pivotally connected to the housing. A protrusion extends outwardly from the arm. The member comprises a threaded rod carried in the aperture of the support. Stops may be threadingly fixed on the rod so as to flank the protrusion, wherein rotation of the rod causes the stop members to engage the protrusion and pivotally move the arm.
In another aspect of the invention the mechanism comprises an apertured support that extends outwardly from the housing. The component comprises a threaded rod carried in the aperture of the support and fastened to the conduit. The member comprises internal threads that engage the rod, wherein rotation of the member against the support causes movement of the rod.
In another aspect of the invention, the mechanism comprises an arm that is pivotally connected to the housing. The member comprises a rack and pinion, one of the rack and pinion being connected to the housing and the other of the rack and pinion being connected to the arm. Motion that is imparted relative to the rack and pinion pivotally moves the arm.
Yet another aspect of the invention is directed to the component comprising at least one plate connected to the conduit. The member is eccentric such that movement of each plate is effected by rotating the member. The mechanism preferably comprises a plurality of plates each containing a conduit opening for receiving the conduit and an opening for receiving the member. A location of the conduit opening in one of the plurality of plates may be offset from a location of the conduit opening in another of the plurality of plates. Each plate comprises an oblong shaped opening that receives the member. Rotation of the member in the oblong shaped opening enables movement of the plate within a predetermined range of distance.
Yet another aspect of the invention is directed to a design method for calculating an optimum adjustment means. The method uses measured geometric data, derived equations, and calculations to configure a throttle ring contour that will reduce P1 to P2 at all flow rates within the adjustment range.
Many additional features, advantages and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows.